The invention relates to a method of calibrating to a desired finished size vehicle wheels made of heat-treatable aluminum sheet.
Vehicle wheels for pneumatic tires are manufactured primarily of steel and in the form of a compound unit consisting of a wheel disk and a rim. The wheel must meet certain conditions with regard to the diameter, circumference, width, depth, and straightness of the rim. After the rim has been formed by rolling, it is fitted onto the wheel disk. Usually, this is accomplished with an expansion die, or alternatively, first with an expansion die which expands the rim further than the required size, and then by compression strain, whereby the rim is pressed onto the wheel disk. This method is less suitable for wheels made of a single piece, e.g., cast or forged aluminum wheels, especially since these wheels are already manufactured with lower tolerances in terms of roundness compared to conventional steel wheels. Therefore, the rims of cast or forged aluminum wheels are frequently cut down to the exact circumferential dimension required to maintain the relatively close tolerances.
In the manufacture of single-piece aluminum wheels by effecting a pressing thereof, it is desirable to preserve the rim in the form in which it was pressed, that is, without calibration to the finished size. For this, cost considerations are on the one hand an essential criterion, but, on the other hand, also much is to be said for the advantageous properties of the metal on the surface produced by pressing. Pressing results in a very uniform distribution of the worked material in the rim and in an extraordinary roundness, which means a slight imbalance. However, subsequent heat treatment can lead to certain changes of shape.
Solution heat treatment such as, for example, described in "Robert B. Ross, Handbook of Metal Treatments and Testing", London, pp. 206-208, is known for improving the material properties of various alloys, including aluminum alloys.
The application of solution heat treatment to wheel rims, too, also has been described in U.S. Pat. No. 3,172,787 in which wheel rims are made of a continuously cast aluminum profile by appropriate rounding and welding. After completion of the welding seam, the rims are solution heat treated, then calibrated to the finished size and configuration in a die. However, this prior art method involves great complexity.